Posts tagged ‘REM’

Assuming you live to the average life expectancy of approximately 67 years, you will spend a phenomenal 208,000 hours sleeping. That equates to just over 20 years sleeping – an entire 33% of your lifespan. Provided you get your 8 hours of sleep a night on average, you’ll dedicate roughly 80,000 hours of that on dreaming (this, however, is extremely approximate as everybody dreams different amounts and enters REM sleep at different times; this will be explained later). Considering we sacrifice 1/3 of our lives to sleep, there must be a reason for it? This article will explore the following:

The 5 stages of sleep, and what happens in each stage.

The reasons we have to sleep, and what would (theoretically) happen if we do not.

An article explaining the Psychology of dreams will be available at a later date.

WHAT HAPPENS WHEN WE SLEEP?

The five stages of sleep and their frequencies.

Sleeping, as described in the introduction, forms a massive part of our life. If you look at the above image, you can see the rough cycle that one would progress through when sleeping. The average human will complete three cycles of sleep in one night. Depending on your own body though, this can range from one cycle to four or five. Before I explain what happens in each stage, it is worthwhile explaining how we test for sleep. By testing electrical impulses in the brain, we can determine what stage someone is in during sleep, The five different stages provoke different brainwaves. It is important to understand these brainwaves in order to appreciate what happens in each of the stages. Consider the following diagram:

Brainwave activity during sleep.

With that diagram here, I can now explain the five stages.

Stage ‘0’ – DrowsinessSometimes this stage is not included in diagrams. This stage is when the human is still entirely conscious, but feels the need to sleep. Consider this to be the point where you say to someone “Wow, I’m shattered!” Brainwaves are random, small and fast (these are not shown on the diagram – visit this link for more detailed brainwaves: http://bit.ly/bS2KAV)

Stage 1 – Very light sleep; practically daydreamingYou could consider this stage as “dozing off”. The eyes begin to roll slightly in the head, and your mind tends to wander a little. Brainwaves at this stage consist mainly of theta waves and occasionally alpha waves (these are present mainly when awake). If your body is ready, and you are free from noise or distraction, you will only be in this stage for a few minutes.

Stage 2 – Light sleepDuring this stage, the brainwave activity changes slightly. Peaks of waves become higher and are slightly more random. Occasionally, “K-Complexes” will occur. These are dramatic and sudden bursts of activity, which result in a very high brainwave. If you note the diagram above, a K-Complex occurs towards the far right of the brainwave for stage 2. K-Complexes occur every 1.0 – 1.7 minutes and are often followed by “sleep spindles” which are bursts of many brainwaves (note the dense area of activity on the far left of the stage 2 brainwave). It seems like K-Complexes occur in response to environmental stimuli, such as noise or touching the skin. The burst of activity may be for the brain to work out whether the situation is dangerous or not, and if so it will wake you up. The heart rate slows during this stage, and body temperature drops slightly.

Stage 3 and 4 – Deep sleep and Very Deep Sleep, respectively.Brainwaves during this are much higher, and less frequent. In stage 3, about 25% of brainwaves are delta waves (the remainder being theta waves). This changes to about 50% delta and 50% theta in stage 4. It is very difficult to wake someone up during this stage of sleep, but if you do, they’ll wake up extremely irritated and moody. Blood flow to the brain decreases, and is focused on muscles – evidence that restoration of other organs and tissue occurs during this stage. The brain is “free” to wander and regain the huge amount of energy used during the day.

Before entering REM sleep (stage 5), the stages reverse. So the person sleeping will go stage 1 – 4, then 4-1 then REM.

Stage 5 – REM sleep; dreams occur here.During this stage the body is paralysed. This is to prevent you from acting out anything you dream – imagine jumping down stairs in real life just because you are dreaming it! Brainwaves revert to being small and rapid – they consist of many beta waves, which are also present when awake. This is support for the idea vivid dreaming is occurring, as the brain is very active. Rapid eye movement occurs quite a lot, and there are occasional muscular twitches. If someone is woken up during this stage, they are MUCH more likely to remember what they were just dreaming. The first time you enter REM during the night, it will only last for about 15 minutes; as the night progresses you spend longer and longer in REM (up to approximately 90 minutes). After, you drift back through stages 1-4, then 4-1 before returning to REM sleep and dreaming again. Dreams can occur in other stages, but they are less vivid, less emotional and less memorable.

WHY DO WE SLEEP?There are a number of theories as to why we sleep:

We need the time to recuperate and “reload” our deposits of energy.

Studies suggest most growth and development occurs during sleep.

Sleep is needed to consolidate information learnt during the day. Studies show that without sleep, people tended to forget more information they learnt previously.

We need sleep to stay in a good mood. Without it, people become irritable and disorientated.

Sleep allows the body to replace red and white blood cells easier.

What happens if we don’t?It has been found (using rats) that lack of sleep can actually lead to death. However, humans will at first begin to experience slowed speech, slow reactions and bad motor functioning. Emotions will cease to the point the person doesn’t care about much and doesn’t react to emotional stimuli. If the person becomes extremely sleep deprived, they will at first experience “micro-sleep”, where by the brain shuts off for 5-10 seconds then ‘boots back up’ again. This is very dangerous and can result in fainting and sickness. If they reach a severe lack of sleep, they will begin to hallucinate as the brain desperately seeks sleep and tries to enter REM. Eventually the person is likely to pass out before they reach a critical, potentially fatal state.